Auto-translated
I completed this mission in a rather unusual way, and expert logistics proved very helpful. With Ilay, without collecting anything, we go around to capture the demonic cities; one step to the left, one step to the right – we won't make it! The hero handles this task quite well; you don't really need to save troops, as we won't need them anymore. After capturing all three cities with Ilay, we move to lift the siege; he barely makes it (only one extra step remains), but we get practically fully built cities, and meanwhile, Isabel captures the mines underground. Well, after that, it's just a matter of technique: break the gold and garrison sums (Wolfsten with Frida should handle it), and take the cities (only for the coins). First, we hire imps (to burn mana), archdevils (only they can jump over walls + summon lords), and demonesses. It's better to storm with Ilay, as the demons won't receive a morale penalty.